Conventionally, a signal removal apparatus of this kind is used for removing signals arriving to the microphone from particular directions in an environment where a plurality of audio/speech signals and noise are spatially mixed. As an example of a conventional signal removal apparatus, a noise suppression apparatus for speech (voice) recognition is described in Patent Document 1. This apparatus is a signal removal apparatus capable of removing a signal even when the signal comes from a direction different from a particular direction expected or the power of a signal coming from the particular direction is close to or less than the power of signals coming from other directions.
FIG. 18 is a block diagram showing the configuration of the noise suppression apparatus for speech recognition disclosed in Patent Document 1. This configuration will be described. The noise suppression apparatus for speech recognition comprises microphones M1 and M2, a frequency analysis unit 41 that extracts the frequency spectrum of a signal on each channel, a phase rotation unit 45 that rotates the phase of the channel 2, an adaptive beamformer 51 that cancels a target voice, a fixed beamformer 52 that cancels a target voice, and a target voice canceled outputs integration unit 54 that integrates outputs of the adaptive beamformer 51 and the fixed beamformer 52. As described, in the apparatus shown in FIG. 18, the outputs of the adaptive beamformer 51 and the fixed beamformer 52 are integrated by the target voice canceled outputs integration unit 54.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-P2003-271191A (FIG. 10)